This invention relates to a cover for a multi-sample container, of a variety known as a "cell culture plate" or a "microtiter plate" for culturing and manipulating living cells. Specifically, the invention concerns cell culture plates in which the plate is sealed with an oxygen and carbon dioxide-permeable waterproof sealing membrane.
Cell culture plates including the so-called "multiwell microliter plates" (herein collectively abbreviated and termed "culture plates" or "plates") are shallow plastic vessels with multiple compartments, i.e., sample wells, which are used for holding growth medium for culturing cells. Culture plates are currently manufactured from polystyrene, polyethylene, polypropylene, polycarbonate, and polyvinyl thermoplastic resins using conventional injection-molding or thermoforming methods. The most common present day culture plates measure approximately 3 inches by 5 inches and are physically described, depicted and commercially available in most scientific supply catalogs (see, for example, Nunc Products 1996 catalog, Nalge Nunc International, Naperville Ill.). Culture plates typically contain between 4 and 384 sample wells per plate. Depending upon the size of wells in a plate, the liquid capacity of each well ranges from approximately 100 microliters to 2 milliliters.
Living cells contained in the sample wells of culture plates can be tested or assayed for physical, chemical and biological properties during or after cell growth using biochemical and immunochemical techniques and reagents. Growth and/or reliable testing of cells in the multiple wells of such plates depends upon the plates being free of cytotoxic substances, ongoing sterility being maintained within the wells of the plates, and uniform dependable oxygen and carbon dioxide exchange into and out of the wells. For maintaining sterility, either of two commercially available covers may be used on the plates during or after cell growth. The covers protect not only living cells within the sample wells, but also their metabolites and any associated sterile reagents added to the wells. The first type of cover is principally used during cell growth, and is a loose-fitting molded plastic lid which overhangs the plate to exclude particulate contaminants (such as bacterial contaminants), while allowing exchange of gases for support of cellular respiration and cell growth. The second type of cover is an essentially gas-impermeable adhesive polyester, polypropylene, or polyethylene plastic sealing film (e.g., Sealplate.TM., manufactured by Excel Scientific, Inc., Wrightwood, Calif.). Such sealing films function to seal each sample well, and prevent well to well contamination and sample evaporation, while being chemically inert so as to allow chemical processing steps to be carried out in the plate. Since this second type of cover is gas-impermeable, it is only applied to the plate following cell growth. It is most useful for freezer storage, preservation, and the chemical processing of cells and other micro-samples.